Aerocapture guidance methods for high energy trajectories

Abstract

This thesis investigates enhancements of an existing numerical predictor-corrector aerocapture guidance algorithm (PredGuid). The study includes implementation of an energy management phase prior to targeting with a generic method of transition and replacement of heuristic features with more generic features. The vehicle response during energy management was modeled as a second-order spring/mass/damper system. Phase change occurred when two conditions were met: First, the vehicle could fly a constant bank angle of 1100 for the remainder of the trajectory and have the resulting apogee below or within a given tolerance above the target apogee. Second, the predicted final energy indicated that the vehicle would be on an elliptical, not hyperbolic, trajectory. So as to incorporate generic features, modeling of a separate lift down phase was replaced by using a lift-down condition to determine phase change and biasing to the same lift-down condition during targeting. Also, use of a heuristic sensitivity to calculate the first corrected bank angle was replaced by a simple 'smart guessing' algorithm. Finally, heuristic lateral corridor boundaries were replaced by boundaries based on percentage of forward velocity. Analysis of the resulting entry corridor revealed that the enhanced algorithm generated a mean improvement of 261% over the PredGuid corridor. Most of the gain occurred for steeper flight path angles. Results also indicated that the enhanced algorithm yielded lower maximum accelerations and comparable heating rates, heating loads, and AV to raise perigee. These results are intended to provide a starting point for further enhancement and applicability to interplanetary travel.